The invention involves a device and a procedure for refractive laser surgery on a target object.
(1) Field of the Invention
(2) Description of the Related Art
Refractive laser surgery is used to correct eyesight defects of the human eye. Defective eyesight is one of humanity's main afflictions. In the developed industrial nations, ophthalmology has developed defective eyesight into a major field of medicine. Alongside the classic forms of eyesight correction, such as spectacles, contact lenses or the implantation of a new lens in the eye, recent years have seen the increasing use of eyesight correction by means of controlled tissue removal (ablation) from the surface of the cornea using laser. The laser most commonly used is the excimer laser. Related techniques include PRK (“Photo Refractive Keratectomy”), LASEK (Laser-In-situ-Keratomileusis) and LASEK (Laser Epithelial Keratomileusis). These involve altering the surface shape and thus the focal distance of the cornea. The procedure used include both so-called “broad beam tissue removal” procedure and “scanning tissue removal” procedures: The scanning procedure involves the use of a scanner device to move the laser beam used in the, treatment across the region of the eye that the treatment is to be performed on.
The LASIK procedure is currently the most commonly applied laser procedure in eyesight correction operations. LASIK is a combination of an operative “cutting technique” (Keramileusis) with PRK. In the LASIK procedure, the first step involves cutting a slice of the cornea (a “flap”), which is then tilted open rather in the manner of the cover of a book. It is then possible to remove the tissue from the cornea using an ultraviolet laser beam (UV laser beam) in order to correct the eyesight defect. At the end of the operation, the cornea slice is closed again. The cutting technique, together with the precision of the laser, permits a high level of accuracy in predicting the results of the treatment, even in cases involving large-scale corrections, as well as a swift recovery.
The application of laser beams with impulses of very short impulse duration in the range of femtoseconds (fs) was proposed for use in incisions into the cornea in the publication U.S. Pat. No. 5,984,916. Procedures have also been developed for so-called intrastromal refractive surgery using ultra-short impulses (Der Ophthalmologe: 98, 2001 623).
The use of fs-impulses to cut the cornea on the one hand, and the use of UV laser beams to remove tissue from the cornea on the other hand, render the application of this treatment method complicated for the user, since two very different laser systems have to be coordinated during the treatment process. The two laser systems have to be set up in such a way that the laser beam scanning the eye does not cause any unwanted damage to the eye. This entails a great deal of effort with respect to the technical apparatus.
The aim of the invention is the creation of an improved device and an improved procedure for refractive laser surgery, ones which are easier for the user in applying the treatment method for correcting eyesight defects and which raise the standard of safety while the operation is being performed.
The aim is fulfilled by the invention in the form of a device as recited in the claims and a procedure as recited in the claims.